How to Split an Existing Mac HFS Volume
Overview
This is being provided primarily for users using our products Scannerz for Mac OS X and Phoenix for Mac OS X to allow them to take an existing volume and add another volume to it, however anyone needing to know how to add another volume to an existing hard drive may find it useful.
Prerequisites
About the only prerequisite is that you have a volume with enough free space on it to allow the creation of another volume, and that the data has been backed up. Although we’ve never seen this process end up ruining an existing volume, that doesn’t mean it can’t happen. As a general rule of thumb, if the volume being split has a bootable operating system installed on it, it’s best to have at least 16GB of free space available on that volume after the volume has been split. If you’re creating a Phoenix Boot Volume, we recommend that the minimum size of the volume be at least 20GB, although users using Lion or Snow Leopard may be able to barely get away with 16GB.
Procedure
The procedure requires using Disk Utility, which is included with the operating system and found in the Utilities folder. For this example, we will be taking an existing Time Machine backup drive and adding another volume. The process is simple, so we’ll describe it in a few steps.
Step 1. Start Disk Utility